1. Field of the Invention
The present invention relates to an optical disk device that writes information on an optical disk and reads information from the optical disk. Further, the present invention relates to a method of adjusting the optical disk device. Particularly, the present invention relates to an optical disk device that can perform accurate tilt adjustment without being affected by an error, and to a method of adjusting the optical disk device.
2. Description of the Related Art
An objective lens focuses laser light to form a light spot on a track of an optical disk in order to perform recording or reproducing. When the optical axis of the objective lens is inclined with respect to the recording surface of the optical disk, optical aberration is generated on the light spot, and as a result, a recording or reproducing problem occurs. For this reason, the inclination of the objective lens with respect to the recording surface of the optical disk has to be as small as possible.
Recently, DVD for reproducing has become widely used, and DVD for recording has been in practical use. Further, the numerical aperture of the objective lens needs to be increased in order to achieve high density recording. Accordingly, it is more required to prevent the objective lens from being inclined from the recording surface of the optical disk.
In an effort to resolve the above problem, Japanese Patent No. 2747332 discloses a technique in which a sensor for detecting the tilt of an optical disk is provided at a part that fixes an optical pickup, and the objective lens holder is deformed by a piezoelectric element in accordance with the detection amount of the sensor so that the objective lens can be made to be inclined for adjustment. In this manner, the inclination of the objective lens from the optical disk can be adjusted.
Since the objective lens and the sensor are separately provided in this case, when the objective lens is inclined to adjust the tilt, the sensor is not moved. Accordingly, the tilt value that the sensor detected does not become zero. The tilt is determined by the detection amount and the sensitivity of the sensor. Inclination control is performed such that the voltage necessary for adjusting the determined disk tilt is applied to the piezoelectric element based on the sensitivity of the objective lens inclination adjustment performed by the piezoelectric element.
However, in the tilt adjustment system (that is not limited to the system using the piezoelectric element) in which the objective lens is not inclined together with the sensor, a tilt adjustment error is caused by a zero point and sensitivity of the sensor, and a zero point and a sensitivity scattering of mechanisms for inclining the objective lens.
For this reason, it is necessary to accurately adjust the position of the sensor, and the position of the mechanism for inclining the objective lens, but an adjustment discrepancy is generated due to the adjustment difference and the circuit offset. Furthermore, the sensitivity scattering of the mechanisms that incline the sensor and the objective lens has to be suppressed as much as possible, but the extent of limitation of such suppression is limited because of the material difference and the gain difference of a detection circuit and a driving circuit.
In addition, when the sensitivity changes as time lapses, the tilt adjustment error increases. Accordingly, in the system in which the objective lens is not inclined together with the sensor, the tilt adjustment cannot be performed adequately.